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  <script>
    //利用递归函数求1-n的阶乘 1*2*3*4*...n
    function fn(n){
      if(n ==1){
        return 1;
      }
      return n * fn(n-1);
    }
    console.log(fn(3));
    console.log(fn(4));
  </script>
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